The present invention relates to anode structures and, more particularly, to anode structures for primary electrochemical cells.
Primary electrochemical cells are generally well known and understood by those skilled in the art. One particularly useful primary electrochemical cell, especially for high current drain applications, is a so-called prismatic primary electrochemical cell. Such a cell is described in detail in U.S. Pat. No. 4,086,397, in the names of Franz Goebel and Nikola Marincic, and includes a battery stack enclosed together with an electrolytic solution within a metal housing. The battery stack as used within the cell comprises a large number of generally rectangular cell components including a plurality of anode structures, carbon cathode current collector electrodes, and insulative separators (e.g., of fiberglass) between the anode structures and the carbon cathode current collector electrodes. Each anode structure generally comprises a large rectangular, flat, single, continuous sheet of an oxidizable alkali metal, such as lithium, physically impressed into a flat supporting expanded metal (e.g., nickel) grid, and each of the carbon cathode current collector electrodes comprises an aggregation of porous, semi-rigid carbon globules or conglomerates physically impressed into a flat expanded metal (e.g., nickel) current collector grid. A common and preferred electrolytic solution employed in the cell as described above is a cathodelectrolyte solution comprising a reducible soluble cathode such as thionyl chloride and an electrolyte solute such as lithium tetrachloroaluminate dissolved in the thionyl chloride.
By the appropriate selection of battery cell components and materials, a cell as described above can be constructed to have any one of several possible sizes and energy configurations. A typical cell, for example, has exterior dimensions of approximately 18 inches (height).times.13 inches (width).times.10 inches (depth), a weight of 156 pounds, an ampere-hour capacity rating of 10,000 ampere-hours, and a nominal discharge current of 40 amperes.
In an electrochemical cell as described hereinabove, it is possible under certain adverse conditions, for example, in the case of severe physical abuse to the cell, for an internal short circuit condition to develop within the cell between metal parts of a pair of anode and cathode structures. In such a case, a hot spot can develop in the lithium sheet of the anode structure and propagate throughout the sheet. If the sheet temperature is high enough, for example, above 180.degree. C., the lithium metal can melt and react violently with the thionyl chloride, or with components of the discharge reaction such as sulfur, or both, resulting in severe, permanent physical damage to the cell.